1. Field of the Invention
The present invention relates to an improved light guide for coupling light output from a light source to the skin, especially to relatively steeply curved areas of the skin. Light guides are described which are suitable for use in cosmetic or therapeutic light treatment apparatus.
2. Description of the Related Art
Apparatus for such use will have a light source capable of a light output sufficient to produce the desired effect when properly directed to the skin of the patient. The light source is typically either a laser or a high intensity flash or continuous source of non-coherent light. In most laser systems the light is directed to the skin by transmission through air without the use of a light guide. In most non-coherent light operated systems (also known as Intense Pulsed Light or IPL System) however, and in some laser systems, the light is transmitted to the skin via a solid light guide which has a light-entry face adjacent the light source and a light exit face which contacts the skin.
Light guides of various shapes are shown in EP-A-0885629, DE-A-3803763, and U.S. Pat. No. 5,620,478. For optical transmission, and skin cooling, it has been proposed to put a gel between the light guide and the skin. Typically, the light guide is a short block of transparent, rigid, solid material which has a flat or curved skin contacting face. Materials used include glass, sapphire, and plastics. One of the advantages of non-coherent light operated systems over laser systems is that it is possible to obtain a suitable light energy flux over a larger area. This reduces treatment time and makes it easier to achieve a uniform light exposure over a large area. However, we have found that whilst the existing rigid light guides are satisfactory in use on relatively ‘flat’ areas of skin, they are less satisfactory when treatment is aimed at relatively highly curved areas of the body, such as the face. The difficulty in treating the face is made more severe by the skin being curved in more than one direction and by the underlying bone structure which prevents the skin being flattened by application of pressure via the light guide.
Failure of good contact between the light guide and areas of the skin can lead to untreated areas or possibly to small burns. The latter appear to result from the light energy which should penetrate down through the skin instead being absorbed in the skin surface layers. Possibly this is due to light rays impinging on the skin at a low angle of incidence.